From 7c2e376938fb94b557b6fa4796de6f65e4966b90 Mon Sep 17 00:00:00 2001
From: Andrew Ekstedt <andrew.ekstedt@gmail.com>
Date: Sat, 23 Dec 2023 07:30:37 +0000
Subject: [PATCH] day 23 part 2

---
 day23/sol2.py | 84 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 84 insertions(+)
 create mode 100644 day23/sol2.py

diff --git a/day23/sol2.py b/day23/sol2.py
new file mode 100644
index 0000000..cd97a9c
--- /dev/null
+++ b/day23/sol2.py
@@ -0,0 +1,84 @@
+import sys
+input = sys.stdin
+map = []
+for line in input:
+    map.append(list(line.strip()))
+
+# construct a graph
+for i,c in enumerate(map[0]):
+    if c == '.':
+        start = (i,0)
+        break
+
+def neighbors(x,y):
+    n = []
+    c = map[y][x]
+    for i,j in [(y-1,x),(y+1,x),(y,x-1),(y,x+1)]:
+        if 0 <= i < len(map) and 0 <= j < len(map[i]):
+            if map[i][j] != '#':
+                n.append((j,i))
+    return n
+
+spots = []
+for i in range(len(map)):
+    for j in range(len(map[i])):
+        if map[i][j] in '.<>v^':
+            n = neighbors(j,i)
+            if len(n) not in (0,2):
+                spots.append((j,i))
+
+def reachable(start,spots):
+    q = [(0,start)]
+    dist = {}
+    r = []
+    while q:
+        q.sort()
+        n,(x,y) = q.pop(0)
+        if (x,y) in dist:
+            continue
+        #print(x,y,neighbors(x,y))
+        if (x,y) in spots and (x,y) != start:
+            r.append((n,(x,y)))
+        else:
+            dist[x,y] = n
+            for j,i in neighbors(x,y):
+                if (j,i) not in dist:
+                    q.append((n+1,(j,i)))
+
+    return r
+
+G = {}
+for p in spots:
+    G[p] = reachable(p,spots)
+
+from pprint import pprint
+pprint(G)
+
+for p in G:
+    if p[1] == len(map)-1:
+        goal = p
+
+print("start=",start)
+print("goal=",goal)
+
+print("brute force...")
+
+
+def longest(p, seen, depth):
+    best = -10000000
+    b = []
+    if p == goal:
+        return  0,[]
+    if p in seen:
+        raise Error("alredy seen")
+    seen.add(p)
+    for n,q in G[p]:
+        if q not in seen:
+            t,path = longest(q, seen, depth+1)
+            if t+n > best:
+                best = t+n
+                b = [q]+path
+    seen.remove(p)
+    return best, b
+
+print(longest(start,set(),0))